The development and characterisation of a laser driven flyer system

• Main Author: Greenaway, M. W.
• Published: University of Cambridge 2000
• Subjects: 535
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599664

A system for the launch of hypervelocity miniature flyer plates has been developed, characterised and applied. A laser-induced plasma is used to drive flyers, typically 5 μm thick and less than 1 mm in diameter, at velocities of a few km/s. Chapter III discusses the implementation of a fibre optic system to manipulate the spatial profile of the laser spot and thus influence the shape of the resultant flyer. A technique and procedure for coupling high power laser pulses into optical fibre has been developed. The surface finish of the fibre was found to be a critical factor. An investigation into surface preparation techniques has been conducted and an optimum procedure developed. Quantitative comparisons of fibres have been made through laser-induced damage threshold measurements and atomic force microscopy. The spatial profile of the emerging light spot was characterised. Altering the length of the fibre was found to be the most effective way of influencing the emerging intensity distribution. This fibre optic system has been successfully used to launch flyer plates and chapter IV describes the technique. Measurements of the flyer performance were made by high-speed streak photography. The flyer was found to show near perfect planarity and achieves velocities approaching 2 km/s. A maximum velocity was achieved within the first 100 μm of flight and sustained up to at least 400 μm. For a comparison, flyers launched with the raw laser pulse have been studied. These flyers were impacted on energetic materials to induce detonation and this work is described in chapter V. The sensitivity of various explosive charges was compared through measuring the threshold laser energy required to launch a flyer of sufficient velocity to initiate detonation. The effect of charge density was found to have a large influence on the laser energy required and an investigation into this has been conducted.